Betty left home at 11.10 a.m. and drove towards the countryside. 3 hours later, her cousin left their home and drove towards the same countryside at 84 km/h. When the cousin reached the countryside at 7.10 p.m., Betty had another 4 km to travel. What was Betty’s average speed? Express your answer in mixed number.
Time that the Betty's cousin started driving = 2.10 p.m.
Duration that Betty's cousin drove from 2.10 p.m. to 7.10 p.m. = 5 h

Distance that Betty's cousin travelled
= 5 x 84
= 420 km

Distance that Betty travelled by the time her cousin reached the city
= 420 - 4
= 416 km

Time that Betty took to travel 416 km = 8 h

Betty's average speed
= 416 ÷ 8
= 52 km/h

Answer(s): 52 km/h